In spite of Vice President Mondale's effort to reassure Israel that the opposite is true, top Israeli officials said yesterday that they expect the United States to step up "unpleasant" pressure for territorial concessions in the West Bank and Gaza Strip.

"We have a feeling that certain steps by the (Carter) administration will be less nice than the speeches by Mondale," one high-level source said just minutes after Mondale left Jerusalem on his wayf to Alexandria to meet with Egyptian President Anwar Sadat.

"The American policy now raises high Egyptian expectations - very high expectations that can be fulfilled only by Israel paying the price." said the official, who asked not to be identified.

While Prime Minister Menachem Begin and other Israeli leaders publicly praised Mondale's visit as a major step in re-establishing U.S. Israelities, several foreign policy makers said they are particulary worried about one passage in a speech Mondale made Monday at a state dinner.

In the speech, Mondale said Israel's peace offer for the Sinai, which involves negotiated withdrawal and minimal security guarantees, is an approach that could be applied to the West Bank and Gaza as well.

Mondale made the suggestion in the context that if there is to be Middle East Peace, "the implicit bargain" of U.N. Security Council resolution 242 must be fulfilled. The resolution calls for Israeli withdrawal from territories captured in the 1967 war.

The official said Israel views the Mondale statement as a threat that the United States will try to link Sinai with the West Bank."

He added, "You cannot separate security and territorial concessions in the West Bank and Gaza. You can try to do it in Sinai, but not in the West Bank and Gaza."

The official noted that in the case of Sinai, Egypt had sovereignty before 1967, but he said Jordan's claim to the West Bank, which it captured in the 1948 war, was "more than contestable."

Drawing a parallel between the Sinai territorial concessions offered to Egypt by Begin and the negotiations over withdrawal from the West Bank and Gaza, the official said, only encourages Sadat to insist upon the complete Israeli withdrawal even before discussions begin on the nature of secure borders. Israel has already rejected that proposition.

"That's why we attach so much importance to this analogy of the Sinai and the West Bank," he said, adding that the Israeli government wants the Carter administration to consider each territory in a different light.

In his speech, Mondale seemed to be specific about applying the Sinai offer to the West Bank and Gaza. He said, "In the Sinai, Israel has proposed a peace treaty in which there would be a negotiated withdrawal and security would be achieved while relinquishing claims to the territory. This approach can be applied in the West Bank and Gaza as well."

In a press conference yesterday however, Mondale attempted to tone down the remark, saying, "We were not arguing that the plan on Sinai automatically applied to the West Bank and Gaza." He added that there are "obviously many differences," presumably in the area of security considerations.

Upon leaving Israel, Mondale stressed that the United States will not apply economic pressure on Israel or threaten to withhold military aid in order to influence Israel's negotiating position, a promise he said to have made privately in meetings with Begin and other Israeli officials.

Mondale also said that the United States and Israel still have many differences of opinion - particulary in interpretation of resolution 242 - but he emphasized that the differences were not based on "animosity or distrust" but are between "good friends."

Zalman Shoval, one of Foreign Minister Moshe Dayan's key advisers and head of the ministry's information committee, said that while Mondale's assurances of the U.S. commitment to Israel were welcomed, "I'm afraid the situation has not changed for the better."

In an Israel radio interview, Shoval added, "Basically, we must be aware of the fact that differences of approaches with respect to the terrritories . . . are as deep as ever.

"We still have a feeling . . . that the pressure is mostly on Israel, and to a very little extent on Egypt, and that this is causing a hardening of Egypt's position," Shoval said.

Another Foreign Ministry official said that all Mondale had done was to "restate" the differences between Israel and the United States and added, "This is to me an indication that the basic differences betweent eh two countries haven't been overcome and also haven't been papered over."